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> > > > - if (WARN_ON_ONCE(!pgmap->ops)) > > - return; > > - > > - if (WARN_ON_ONCE(pgmap->type != MEMORY_DEVICE_FS_DAX && > > - !pgmap->ops->page_free)) > > + if (WARN_ON_ONCE((!pgmap->ops && > > + pgmap->type != MEMORY_DEVICE_GENERIC) || > > + (pgmap->ops && !pgmap->ops->page_free && > > + pgmap->type != MEMORY_DEVICE_FS_DAX))) > > Playing around with dcssblk, adding devm_memremap_pages() and > pgmap.type = MEMORY_DEVICE_FS_DAX, similar to the other two existing > FS_DAX drivers drivers/nvdimm/pmem.c and fs/fuse/virtio_fs.c, I hit > this warning when executing binaries from DAX-mounted fs. > > I do not set up pgmap->ops, similar to fs/fuse/virtio_fs.c, and I don't see > why they would be needed here anyway, at least for MEMORY_DEVICE_FS_DAX. > drivers/nvdimm/pmem.c does set up pgmap->ops, but only ->memory_failure, > which is still good enough to not trigger the warning here, probably just > by chance. Yes, I think so. And you can guess which driver I've done all my testing with. > Now I wonder: > 1) What is this check / warning good for, when this function only ever > calls pgmap->ops->page_free(), but not for MEMORY_DEVICE_FS_DAX and > not for MEMORY_DEVICE_GENERIC (the latter only after this patch)? > 2) Is the warning also seen for virtio DAX mappings (added Vivek and > Stefan on CC)? No pgmap->ops set up there, so I would guess "yes", > and already before this series, with the old check / warning. Right, I simply updated the warning to reflect what should have been happening prior to this change. However looking again I don't think free_zone_device_folio() is ever called for MEMORY_DEVICE_FS_DAX pages. Instead put_devmap_managed_folio_refs() would have returned false and cause most paths to skip calling free_zone_device_folio(). The only path that doesn't do that appears to be `folio_put()`. That probably should also be calling put_devmap_managed_folio_refs(), I'm not sure why it doesn't. > 3) Could this be changed to only check / warn if pgmap->ops (or maybe > rather pgmap->ops->page_free) is not set up, but not for > MEMORY_DEVICE_GENERIC and MEMORY_DEVICE_FS_DAX where this is not > being called? Oh I think I know what actually happened. Earlier versions of my patch series did define a pgmap->ops->page_free() callback for MEMORY_DEVICE_FS_DAX but review comments suggested I just do all the was required directly in the switch statement. Obviously I forgot to update the check when I removed the need for pgmap->ops->page_free and having pgmap->ops->memory_failure defined was sufficient to (accidentally) get past the check. So yeah, the check is wrong. It shouldn't require pgmap->ops to be defined for MEMORY_DEVICE_FS_DAX or MEMORY_DEVICE_GENERIC. > 4) Or is there any reason why pgmap->ops would be required for > MEMORY_DEVICE_FS_DAX? Nope. > Apart from the warning, we would also miss out on the > wake_up_var(&folio->page) in the MEMORY_DEVICE_FS_DAX case, when no > pgmap->ops was set up. IIUC, even before this change / series (i.e. > for virtio DAX only, since dcssblk was not using ZONE_DEVICE before, > and pmem seems to work by chance because they have ops->memory_failure). See __put_devmap_managed_folio_refs() - the wake_up_var() was there to intercept the 2->1 refcount transition. Now the wake_up_var() needs to happen on 1->0, hence why it got moved to free_zone_device_page(). > > return; > > > > mem_cgroup_uncharge(folio); > > @@ -494,7 +493,8 @@ void free_zone_device_folio(struct folio *folio) > > * zero which indicating the page has been removed from the file > > * system mapping. > > */ > > - if (pgmap->type != MEMORY_DEVICE_FS_DAX) > > + if (pgmap->type != MEMORY_DEVICE_FS_DAX && > > + pgmap->type != MEMORY_DEVICE_GENERIC) > > folio->mapping = NULL; > > > > switch (pgmap->type) { > > @@ -509,7 +509,6 @@ void free_zone_device_folio(struct folio *folio) > > * Reset the refcount to 1 to prepare for handing out the page > > * again. > > */ > > - pgmap->ops->page_free(folio_page(folio, 0)); > > Ok, this is probably the reason why you adjusted the check above, since > no more pgmap->ops needed for MEMORY_DEVICE_GENERIC. > Still, the MEMORY_DEVICE_FS_DAX case also does not seem to need > pgmap->ops, and at least the existing virtio DAX should already be > affected, and of course future dcssblk DAX. > > But maybe that should be addressed in a separate patch, since your changes > here seem consistent, and not change or worsen anything wrt !pgmap->ops > and MEMORY_DEVICE_FS_DAX. Nah, I think the check is wrong and needs fixing here. > > folio_set_count(folio, 1); > > break; > > > > For reference, this is call trace I see when I hit the warning: Well thanks for testing this and for posting these results. > [ 283.567945] ------------[ cut here ]------------ > [ 283.567947] WARNING: CPU: 12 PID: 878 at mm/memremap.c:436 free_zone_device_folio+0x6e/0x140 > [ 283.567959] Modules linked in: > [ 283.567963] CPU: 12 UID: 0 PID: 878 Comm: ls Not tainted 6.14.0-rc3-next-20250220-00012-gd072dabf62e8-dirty #44 > [ 283.567968] Hardware name: IBM 3931 A01 704 (z/VM 7.4.0) > [ 283.567971] Krnl PSW : 0704d00180000000 000001ec0548b44a (free_zone_device_folio+0x72/0x140) > [ 283.567978] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3 > [ 283.567982] Krnl GPRS: 0000000000000038 0000000000000000 0000000000000003 000001ec06cc42e8 > [ 283.567986] 00000004cc38e400 0000000000000000 0000000000000003 0000000093eacd00 > [ 283.567990] 000000009a68413f 0000016614010940 000000009553a640 0000016614010940 > [ 283.567994] 0000000000000000 0000000000000000 000001ec0548b416 0000016c05da3bf8 > [ 283.568004] Krnl Code: 000001ec0548b43e: a70e0003 chi %r0,3 > 000001ec0548b442: a7840006 brc 8,000001ec0548b44e > #000001ec0548b446: af000000 mc 0,0 > >000001ec0548b44a: a7f4005f brc 15,000001ec0548b508 > 000001ec0548b44e: c00400000008 brcl 0,000001ec0548b45e > 000001ec0548b454: b904002b lgr %r2,%r11 > 000001ec0548b458: c0e5001dcd84 brasl %r14,000001ec05844f60 > 000001ec0548b45e: 9101b01f tm 31(%r11),1 > [ 283.568035] Call Trace: > [ 283.568038] [<000001ec0548b44a>] free_zone_device_folio+0x72/0x140 > [ 283.568042] ([<000001ec0548b416>] free_zone_device_folio+0x3e/0x140) > [ 283.568045] [<000001ec057a4c1c>] wp_page_copy+0x34c/0x6e0 > [ 283.568050] [<000001ec057ac640>] __handle_mm_fault+0x220/0x4d0 > [ 283.568054] [<000001ec057ac97e>] handle_mm_fault+0x8e/0x160 > [ 283.568057] [<000001ec054ca006>] do_exception+0x1a6/0x450 > [ 283.568061] [<000001ec06264992>] __do_pgm_check+0x132/0x1e0 > [ 283.568065] [<000001ec0627057e>] pgm_check_handler+0x11e/0x170 > [ 283.568069] Last Breaking-Event-Address: > [ 283.568070] [<000001ec0548b428>] free_zone_device_folio+0x50/0x140 > [ 283.568074] ---[ end trace 0000000000000000 ]--- >